Homogenization Diffusion
The thermally activated concentration equalization of alloying elements to eliminate macrosegregation. It ensures a uniform chemical composition throughout the entire component volume.
During welding, diffusion ensures that alloying elements in the material balance out. Atoms move from areas of high concentration to areas of low concentration, and this happens faster the hotter the material is. If the material cools too quickly after welding, this balancing remains incomplete. Then so-called segregations remain, i.e., areas with different compositions. This makes the structure non-uniform, and the weld can become brittle or crack later in service. To ensure the elements distribute well, you need to choose the heat input so that the area around the weld stays hot long enough. For critical materials, it helps to let the weld cool slowly after welding, for example by preheating or post-weld heat treatment.